Final answer:
The Paleozoic marine paleoenvironments included metazoans with planktonic lifestyles such as pteropods and dinoflagellates. Planktonic organisms swam or floated in the water column, while benthic organisms lived on the ocean floor.
Step-by-step explanation:
The student's question pertains to the group of metazoans that exhibited a planktonic mode of life during the Paleozoic era. During this era, marine paleoenvironments were teeming with life, and various organisms had different modes of life, which included being sessile, motile, benthic, and planktonic. Planktonic organisms, unlike benthic ones, did not live on the ocean bottom but floated or swam in the water column.
The Paleozoic era, particularly the Cambrian period, saw a notable increase in marine biodiversity including the rise of planktonic species. Among planktonic species were pteropods, which are small snail-like organisms that used their modified foot to maintain their position in the water column. Planktonic life also included various groups such as dinoflagellates, which are an important component of marine plankton. Dinoflagellates, for instance, are mostly marine and can be phototrophic, heterotrophic, or mixotrophic. They sustain themselves and contribute to the marine food web through different forms of nutrition, including photosynthesis.